The cities in the firing line for the next Hurricane Harvey

Hurricane Harvey on its way to Texas on Aug 25, 2017 (NASA photo, via Getty Images)

“This event is unprecedented & all impacts are unknown & beyond anything experienced.” This was the extraordinary tweet from the U.S. National Weather Service as the flooding from Hurricane Harvey began.

Harvey may have been unprecedented, but it certainly was not unexpected. Houston frequently experiences flooding and experts have repeatedly warned that worse could be to come as the world gets warmer. And yet Houston was shockingly unprepared, not least because its flood control directors think talk of climate change is a plot to prevent development, and its planning system fails to prevent building in the most at-risk areas.

Path of Hurricane Harvey which struck Texas coast on Aug 25, 2017 and again on Aug 30 (New York Times)

It is only a matter of time before more “unprecedented” flooding hits the U.S. Next in the firing line could be other major cities such as Miami, New York and Boston. Yet relatively little is being done. On the contrary, just days before Harvey struck, Donald Trump rescinded rules that mean federal infrastructure projects must take into account flood risks related to climate change.

“The policy direction is to go backwards,” says Charles Iceland of the World Resources Institute in Washington DC. The U.S. should be investing more in flood protection for its growing population and sprawling cities, he says. And climate change will only bring increasingly severe flooding events.

The climate link

Global warming may not have caused Hurricane Harvey to form, but it made the storm worse. Abnormally warm waters in the Gulf of Mexico fuelled the hurricane’s rapid intensification, enabling it to pump extraordinary amounts of moisture into the air over Texas.

Sea levels have risen 0.2 metres over the past century due to global warming. This also compounded the situation, slowing the drainage of flood waters and making the storm surge higher.

Finally, Harvey stalled for a long time after coming ashore, so huge amounts of rain fell in one area. This too might be linked to climate change. A growing number of studies suggest this makes weather systems increasingly likely to get “stuck”, which can lead to extreme rainfall – or extreme heat and drought.

All these factors will conspire to increase the number and severity of extreme flooding events as global surface temperatures soar past 2°C above pre-industrial in the next few decades.

As the air gets warmer, it will hold more moisture, causing more rain (or snow) to fall at certain times. Rising seas will massively increase the threat posed by storm surges, as well as directly causing flooding and erosion – and global sea level could rise more than 2 metres by 2100, according to some recent studies.

Swamped cities

So who is in the firing line?

Iceland runs the Aqueduct project, which assesses countries’ susceptibility to floods. In terms of the number of people at risk, populous countries like India, Bangladesh and China naturally top the project’s tables. Millions are already being affected by river flooding every year.

However, a different picture emerges when looking at the financial cost of flooding. American cities feature prominently in a list of the coastal cities facing the biggest losses from flooding by 2050, according to a 2013 study. The top five are Guangzhou, Miami, New York, New Orleans and Mumbai.

In general, rich cities such as Amsterdam have much better flood protection than poorer cities in developing countries, the study says. But many wealthy American cities have low protection levels.

Hold back the tide

It is clear the U.S. needs to do far more to keep its people and cities safe.

The obvious course is to stop building homes – and chemical factories – in harm’s way. This is not just a problem in Houston: since the 1960s, the U.S. has provided cheap, subsidised flood insurance that has encouraged development in high-risk areas. This scheme’s $24 billion debt is set to soar thanks to Harvey.

Big infrastructure projects have a part to play, too. Massive barrier schemes similar to the one protecting London have long been considered for protecting places such as New York City, but have yet to get the go-ahead.

But it is simply not feasible to protect many areas, such as the vast swathes of Florida set to disappear under the waves over the next century. “There is not much to do except to abandon those areas,” says Iceland.

The strange future Hurricane Harvey portends

Climate change is pushing more water into the atmosphere—with bizarre consequences.

Humans have begun an international project to move water around the world, far more ambitious than any network of aqueducts or hydroelectric dams ever constructed or conceived. The drivers of this global system are billowing vapors, which trap heat and propel the world’s water faster and farther around the globe. The first results of this project may already be seen in the outrageous rainfall totals of storms like Hurricane Harvey, or in landslides on remote mountain hillsides, and even in the changing saltiness of the oceans.

The Earth system is getting warmer. Water is evaporating faster. There’s more of it in the air. It’s moving through the system faster. As a result, the coming centuries will play out under a new atmospheric regime, one with more extreme rain, falling in patterns unfamiliar to those around which civilization has grown.

“Basically the idea is that as the climate warms there’s more energy in the atmosphere,” says Gabriel Bowen, a geochemist at the University of Utah. “That drives a more vigorous water cycle: Evaporation rates go up, precipitation rates go up—there’s just more water moving through that cycle faster and more intensely.”

For each degree Celsius of warming the atmosphere is able to hold six per cent more water. For a planet that’s expected to warm by four degrees by the end of the century, that means a transition to a profoundly different climate.

“Rainfall extremes have increased in intensity I think at every latitude in the northern hemisphere,” says Massachusetts Institute of Technology climate scientist Paul O’Gorman.

In 2012, a study led by Lawrence Livermore National Laboratory oceanographer Paul Durack found that the global water cycle was actually speeding up at twice the rate predicted by climate models, likely intensifying by 16 to 24 per cent by the end of the century.

There will be ever wilder extremes in drought and aridity.

Amazingly, this same signal of a turbocharged water cycle has been pulled out of fossils from deep in Earth’s history during the alien greenhouse climates of the ancient past. These were much different worlds, with antarctic forests and warmth-loving reptiles at the poles—balmy interludes driven by naturally higher carbon dioxide in the atmosphere. Researchers, using proxies as inventive as fossilized sea-cow teeth, have deciphered the chemistry of these ancient oceans, finding in them seas similarly swinging between intensely fresh and salty regions, the signature of the more intense water cycle of a greenhouse planet. We’re a long way from the ancient greenhouse of 50 million years ago, but Durack’s work implies that in the coming decades, in places where evaporation on the planet is strongest, there may be ever wilder extremes in drought and aridity. And where that water eventually falls out of the sky, episodes of unprecedented precipitation.

Hurricane Harvey was a truly one-off storm, one whose unusual path—strangely stalling out over East Texas for days—can explain much of its destructiveness. But imagine if, in its sojourn over Houston, Harvey had dumped out 25 per cent more rain, as O’Gorman and colleagues have forecast is possible by the end of the century. In the tropics, rainstorms may well become even wilder.

But perhaps even more important than how fast water is moving through the system is where it may move thanks to human intervention. The Intertropical Convergence Zone is a band of precipitation that flirts with the equator—where the trade winds meet in the tropics and hot air rises, dumping out prodigious amounts of rain. The ITCZ feeds monsoons and, throughout history, entire civilizations. Its position on the planet has meant life or, in the case of Classic Mayan civilization, perhaps death. Their collapse is linked to a subtly shifting ITCZ and the droughts that followed. And the movement of the ITCZ under a warming climate, and the waters it carries, is one of the most urgent and unresolved questions in climate modeling today, with some forecasts calling for dramatic shifts and expansions.

Eleven thousand years ago in China, strong monsoon rains filled a gigantic Lake Dali and northern China greened, as documented in a recent study led by Columbia university researcher Yonaton Goldsmith. Six thousand years later, the monsoon shifted hundreds of miles to the south, the rains halved, and the lake shriveled up. Ancient Chinese societies, the Hongshan and Yangshao, scattered and collapsed, while politically complex cultures in central China blossomed.

The response of this monsoon to warming, one that holds the fate of Southeast Asian agriculture in the balance, is a similarly unresolved question in climate modeling. Some models show the monsoon strengthening, others show it migrating far from its familiar haunts.

Around the same time as northern China was blossoming in the early Holocene, so too was Earth’s most desolate desert. The African Humid Period brought rains to the Sahara, perhaps the result of more sunlight in the northern hemisphere as the Earth carried on its celestial wobble. Today, by warming the northern hemisphere faster than the southern hemisphere, humans may well again bring more water to this, the world’s largest desert, greening its wastes once more. If so, and perhaps quite unexpectedly, the hurricanes that hit our shores a hemisphere away could become more frequent and intense. A verdant Sahara, by reducing the amount of dust wafting out over the ocean, will allow the sun to beat down on the Atlantic more intensely, forging more powerful cyclones. The idea that shifting rains might turn deserts in Africa to green, spurring more intense hurricanes that will eventually hit North America, illuminates the Rube Goldberg connections of the climate system, and proves there may be more than a few surprises in store as the world changes.

Committing to profound climate change means embracing a leap into the unknown. But that doesn’t mean that more water vapor in the air will necessarily beget a uniformly wetter, more stormy world. Strangely, while the atmosphere is growing more suffused with water vapor, it may also be getting more arid on land in much of the world.

In recent years the relative humidity over land has been falling, a trend that may increase in the future, even as the atmosphere sucks up more water vapor. This isn’t as paradoxical as it sounds. Though the planet’s air as a whole is getting warmer, and warmer air can hold more water, land is warming up much faster than the ocean, and the hotter air above the land isn’t evaporating as much water as the air over the oceans. As a result, even as the atmosphere sucks up water and absolute humidity on land rises, bringing intolerable conditions to humanity in some parts of the world, relative humidity—how much water air can hold at a given temperature—isn’t keeping up over land, the air doesn’t saturate, and it doesn’t rain. Even stranger, this fall in relative humidity may be mediated by plants, which have already changed their physiology in response to our newly high-CO2 world.

It’s well-known that in rain forests, plants and trees actually create their own weather, by opening their pores to take in CO2 and breathe out oxygen. In doing so, they lose vast amounts of water vapor to the air above. That water then rains out of the sky in a perpetual hydraulic dance between life and the air around it. In fossil leaves from the greenhouse climates of the geological past, and in modern laboratories, plants have been shown to reduce the number of pores on their leaves in response to high atmospheric CO2, sipping from the surfeit of carbon dioxide around them, and becoming stingier with the amount of water they give up to the atmosphere. In fact, scientists at Indiana University Bloomington and Utrecht University found that in the past 150 years, plants have reduced the number of pores they use to breathe by 34 per cent. This adaptive change vastly limits the amount of water plants release to the air around them, perhaps contributing to the mysterious fall in relative humidity, and the potential for future aridification.

All of this would seem to indicate that we’re headed toward a largely more arid world but also one with far more water vapor in the air for the occasional devastating storm to sweep up, bringing unprecedented bursts of floodwaters. And in parts of the tropics, perhaps a coming deluge unlike any witnessed by humanity.

Still, on a world as ancient as ours, there are precedents for even the most extreme changes if one looks far enough back into the past. 56 million years ago, at the boundary between the Paleocene period and the Eocene period, in an already very balmy world, volcanoes released amounts of carbon dioxide equivalent to all the world’s fossil-fuel reserves in a matter of a few thousand years. As a result, the water cycle jackknifed, a signal starkly visible in the rocks.

“We go from a system where you have sediment building up slowly over time to these megafan deposits which we only see in places that receive really extreme seasonal precipitation in the modern world.”

Bowen has found the similar signature of raging floods in Big Bend National Park from the same global-warming event. But elsewhere, like in Bighorn Basin in Wyoming, the same interval produces a more arid landscape sparse with vegetation. The starting states in the Eocene and in our modern chemistry experiment with the atmosphere were wildly different, a disparity that would seemingly limit the ancient event’s usefulness as a guide to the coming decades. But Bowen says there are still lessons we can take from it.

“I think you need to look at the delta, or the type of change that we see, as we go into these [past warming events] because we know that we’re forcing the system by adding carbon to it, and we can see just what the pattern of change is over that base condition,” he says. “That’s not to say that we expect that starting from where we are today is going to be identical, but it gives us really our only experimentally based look at how the system responds to that kind of push.”

For the past few thousand years we have lived on a planet unreasonably cozy for civilization. We return to these ancient worlds only foolishly.

“The worst-case scenario is that we see Harveys happen not once in a lifetime but routinely every summer in multiple places, and it’s exacerbated by the fact that sea level is rising rapidly,” says Bowen. “And then we see many of the agricultural areas of the world—sunny places with marginal water availability—become dust bowls.”

Roger Annis is a longtime socialist and trade union activist. He began his political activism with the Young Socialists of the day in Nova Scotia while at university. Since then, he has lived in most regions of Canada, including in Montreal where he became fluent in French. He is a retired aerospace worker living in Vancouver. Roger writes regularly on topics of social justice and peace.